Adware
The most common type of spyware. These are small programs which sit on your computer waiting for you to go online. Once the adware detects that you’re connected to the Internet it starts sending you popup, popover and popunder ads for anything from airline tickets to porn site membership. Not only that but information on your viewing habits is then sold on to marketing companies who will then send you more junk email and popup ads than you ever thought possible.
Browser Hijacker
These are just plain annoying. These install themselves on your computer and change your default homepage and search engine to something else. Every time you start your web browser it will bring you to a page filled with ads, porn or other unwanted material. This interrupts your web browsing and is intensely annoying. Most browser hijackers are also data miners. A data mining program reports your web browsing habits to a central database. This information is then sold on to marketing companies.
Keyboard Logger
These programs are designed for one thing – theft. When you log in to your online banking these can record your PIN number. When you check your private email account these programs can record your password. Keyboard loggers are potentially one of the most damaging pieces of spyware because of the potential financial dangers and theft of personal information.
Modem Hijacker
Potentially the most costly spyware. Modem hijackers are also referred to as diallers. Diallers normally install themselves to your computer via a virus infection or from warez, mp3 or adult websites. A dialler is a small piece of software that will dial long distance, premium rate phone numbers when you’re not at your PC. These phone numbers are normally for adult chat line services located in Russia, China, South America and the Phillipines. I have personally seen unlucky victims receive $2,000 bills for one month of telephone calls.